1. Technical Field
The invention relates to a vibration device, an oscillator having the same, and an electronic apparatus, and more particularly, to a vibration device, an oscillator, and an electronic apparatus with an excellent frequency-temperature characteristic.
2. Related Art
In a piezoelectric device, particularly, a surface acoustic wave (SAW) device, it is known that a frequency-temperature characteristic is improved by using resonance in a top end mode of a stop band.
As disclosed in Pamphlet of International Publication No. 2010-098139, it is conceivable to provide a SAW resonator in which a groove is provided between electrode fingers of the IDT when the IDT capable of excitation in the top end mode of a stop band is formed on a quartz substrate cut to a specific cutting angle, and a groove depth G or a line occupancy η of an electrode finger is appropriately set. If the SAW resonator is manufactured according to the conditions described in Pamphlet of International Publication No. 2010-098139, it is possible to obtain an excellent frequency-temperature characteristic and improve an environmental-resistant property and a Q value.
There is known a technique of combining two frequency-temperature characteristics by electrically connecting two SAW resonators to improve a frequency-temperature characteristic. For example, in the technique disclosed in JP-A-9-298446, the frequency-temperature characteristic curve obtained in the combined state is flattened by horizontally combining two SAW resonators having different peak temperatures on a 2nd-order function temperature characteristic. In addition, as disclosed in G. Martin, H. Schmidt B. Wall “IMPROVED TEMPERATURE STABILITY OF ONE-PORT SAW RESONATORS ACHIEVED WITHOUT COILS”, 2007 IEEE Ultrasonics Symposium, p 925-928, it is conceivable to connect two single-port SAW resonators successively to improve the frequency-temperature characteristic. Specifically, inductors are connected to each single-port SAW resonator in parallel, or the corresponding inductor is excluded (a parallel capacitor may be included).
Using the piezoelectric device having the aforementioned configuration, it is possible to improve the frequency-temperature characteristic compared to the SAW device in the related art. However, although the SAW device disclosed Pamphlet of International Publication No. 2010-098139 has a 3rd-order temperature characteristic, the frequency variation is within ±25 ppm in a temperature range of −40° C. to +85° C. In the SAW devices disclosed in JP-A-9-298446 and proposed by G. Martin et al., the frequency variation increases further.